Associations of timing of physical activity with all-cause and cause-specific mortality in a prospective cohort study

There is a growing interest in the role of timing of daily behaviors in improving health. However, little is known about the optimal timing of physical activity to maximize health benefits. We perform a cohort study of 92,139 UK Biobank participants with valid accelerometer data and all-cause and cause-specific mortality outcomes, comprising over 7 years of median follow-up (638,825 person-years). Moderate-to-vigorous intensity physical activity (MVPA) at any time of day is associated with lower risks for all-cause, cardiovascular disease, and cancer mortality. In addition, compared with morning group (>50% of daily MVPA during 05:00-11:00), midday-afternoon (11:00-17:00) and mixed MVPA timing groups, but not evening group (17:00-24:00), have lower risks of all-cause and cardiovascular disease mortality. These protective associations are more pronounced among the elderly, males, less physically active participants, or those with preexisting cardiovascular diseases. Here, we show that MVPA timing may have the potential to improve public health.


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The sex information is acquired from central registry at recruitment, but in some cases updated by the participant. Hence it may contain a mixture of the sex the National Health Service (NHS) had recorded for the participant and self-reported sex. Taking morning group as a reference, both the midday-afternoon and mixed timing groups, but not evening group, showed significantly decreased risks of all-cause and CVD mortality. We also conducted multiplicative and additive interaction analyses, joint associations, and subgroup analyses on sex. We found that the observed protective effects of the middayafternoon and mixed timing groups seemed to be stronger among males than females.
92,139 UK Biobank participants (mean age, 62 years; 56% female) with valid accelerometer data were recruited. The baseline characteristics of 92,139 participants are shown in Table 1. Overall, four timing groups presented similar profiles for sociodemographic, lifestyle, and health status. However, mixed group showed a lower Townsend deprivation index than other groups. The morning group had a lower education level than other groups. The evening and mixed groups tended to have shorter sleep duration, since they were more from the group of <7 hours/day than morning and midday-afternoon groups. The morning group were more from the group of sleep midpoint earlier than 02:30 than other groups. Additionally, we found that morning and evening groups had fewer moderate-to-vigorous intensity physical activity minutes than other two groups. This is a cohort study that assesses the exposure-outcome associations. in this case, the sample size is determined by the number of events required to perform multivariable regression models. According to the rule-of-thumb estimation, at least ten events are required per variable (including dummy variables) in the model (Riley et al. BMJ. 2020). In the fully adjusted models, we included a total of 24 variables (including dummy variables) in the Cox regression models. Thus, at least 240 events for each outcome were required. The events for all-cause mortality, cardiovascular mortality, and cancer mortality were 3088, 1076, and 1872, respectively. Therefore, the sample size of this study should be sufficient.
The data exclusion criteria were pre-established and documented in Methods and Supplementary Methods. The exclusion criteria are as follows: 1) those who withdrew from UK Biobank; 2) those who had no physical activity data in any one hour of the 24-hour cycle; 3) Similar to the previous study, those who had high nocturnal activity (>10% physical activity accumulated between 01:00 and 04:00), as we focused on individuals with a diurnal lifestyle; 4) those with unreliable or invalid accelerometry data: i) unexpectedly small or large size (UK Biobank Field ID: 90002); ii) less than 72 h or did not provide data for all 1-h periods within a 24-h cycle during the 7-day data collection (Field ID: 90015); iii) not well-calibrated (Field ID: 90016); iv) recalibrated using the previous accelerometer record from the same device worn by a different participant (Field ID: 90017); v) data with a non-zero count of interrupted recording periods (Field ID: 90180); vi) data with more than 768 (Q3 + 1.5 × IQR) data recording errors (Field ID: 90182). In total 11,543 participants were excluded. Finally, 92,139 participants (88.87%) with valid data were included in the current study.
This is a population-based cohort study, and we have not yet replicated the findings in other samples. However, we used different statistical